Exhaust gas reactor

ABSTRACT

Hydrocarbon, carbon monixide, and nitrogen oxide pollutants emitted by post oxidation type exhaust gas reactors can be substantially reduced by redirecting the exhaust gases as they enter the reactor through the use of deflectors of special design and the optional use of improved means for directing the gases onto said deflectors.

United States Patent [191 Rosenlund EXHAUST GAS REACTOR [75] Inventor: Iver T. Rosenlund, Kennett Square, Pa.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Dec. 9, 1971 [21] Appl. No.: 206,351

[52] US. Cl. 60/282, 60/323, 23/277 C [51] Int. Cl. F01n 3/10 [58] Field of Search 60/282, 323;

[56] References Cited UNITED STATES PATENTS 8/1969 Aronsohn 23/277 C X 2/1967 Pahnke et a1. 60/302 Aug. M, 1973 3,413,803 12/1968 Rosenlund et a1. 60/282 X 3,201,338 8/1965 Pennington 23/277 C X 3,653,205 4/1972 Tadokoro 60/322 Primary Examiner-Carlton R. Croyle Assistant Examiner-Robert E. Garrett Attorney-John R. Powell 5 7] ABSTRACT 11 Claims, 6 Drawing Figures 1 //Al I\3 I I, l

Patented Aug. 14, 1973 3,751,920

2 Sheets-Sheet l FIGQZ Patented Aug. 14, .1973 3,151,920

2 Sheets-Sheet 2 EXHAUST GAS REACTOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improvements in oxidation type non-catalytic exhaust gas reactors, which improvements reduce the emission of hydrocarbons, carbon monoxide, and nitrogen oxides from such reactors serving internal combustion engines.

2. Description of the Prior Art Exhaust gas reactors are known which operate to mix air in at least stoichiometric amount with hot exhaust gases thus to oxidize hydrocarbons and carbon monoxide therein. to. relatively innocous products.

Tifft in U.S. Pat. No. 2,263,318 describes a means for introducing air into the exhaust gases of gasoline engines in the region of the exhaust valve, recognizing the importance of providing the air to a region of high temperature to ensure the oxidation of unburned components of the exhaust gas.

Tifft's devices utilize air injected. into the exhaust passages within the-engine block. In automobile engines not equipped with Tifft devices, air is commonly injected slightly downstream from the exhaust valve in modified exhaust manifolds.

Subsequent modifications in exhaust gas reactors improved the performance of Tifft devices and related dc vices by providing means for retaining the exhaust gases at high temperatures for a longer period of time. This beneficial effect is generally achieved by requiring the hot gas mixture to pass through an insulated space, often. in: devices wherein the gases describe folded paths through concentric annuli of multiple wall devices. General turbulence is generated in existing devices by baffles and by sharp changes in direction irriposed on the gas stream. Examples of such devices are found in U.S. Pat. Nos. 3,302,394 and 3,413,803.

Copending application Ser. No. 63,101 filed Aug. 12, 1970, now U.S. Pat. No. 3,633,368 discloses improvements over U.S. Pat. No. 3,413,803 which comprise alternate predominant paths for the exhaust gases appropriate to various gas flow rates corresponding to various conditions of operation of an automobile. The exhaust gas reactor of U.S. Pat. No. 3,413,803 is structured as a group of three concentric tubes surrounding two annuli, an inner annulus between the innermost tube, hereinafter called the core, and the middle tube, andan outer annulus between the middle and outer tubes, the core into which the exhaust gases enter, having peripheral openings to the inner annulus, the middle tube being open at its ends and provided with a bypass hole, and the exterior tube being insulated and open only at a gas outlet, all arranged to provide a path of flow which is predominantly from the core through the two annuli in series and out the outlet of the exterior tube when the gas flow rate is relatively high,.and a shorter path from the core through the two annuli via the bypass holes to the outlet which predominates when the gas flow is relatively low. These improvements function well to provide reduced emissions, however there is continuing pressure from government agencies and the interested public for even lower emissions.

The reduction of hydrocarbon and carbon monoxide levels in exhaust gases in reactors pertinent to this invention is generally agreed to depend on their oxidation to carbon dioxide. The rate of the oxidation of these hydrocarbons and of carbon monoxide and thus the thoroughness of their conversion during their brief residence in exhaust gas reactors is exponentially temperature dependent. For this reason even brief extension of the high temperature condition of the gases is accompanied by surprising reduction in the emission of these pollutants. However, even brief extension of the high temperature condition is difficult to achieve by art means such as insulation.

It is the object of this invention to provide an improvement to exhaust gas reactors comprising a core, which improvement provides extension of high temperature conditions with a concomitant reduction in hydrocarbon, carbon monoxide, and nitrogen oxide emissions below those obtainable with exhaust gas reactors of the prior art.

SUMMARY OF THE INVENTION In summary, this invention is directed to an improved exhaust gas reactor for reducing the undesirable emissions from an internal combustion engine, said reactor comprising an elongated casing having inlet holes, an outlet, and a core into which the exhaust gases enter, said improvement comprising (a) a curved gas deflector, positioned within said core across from and in concave relationship to the exhaust gas inlet to the core, said deflector being positioned such that the angle [3 of the tangents at the intersection of the deflector and the core wall is no less than 20 and no more than and the ratio of the core radius to deflector radius is between 0.5 and 2.5. It has been found that one or two gas deflectors essentially circular shaped in cross section, positioned within the core across from and in concave relationship to the exhaust gas inlet to the core, deflect the incoming exhaust gases and air mixture so as to minimize scrubbing heat transfer contact with the core walls and thus retain the gases for a longer period of time at or near their initial high temperature. This effect is heightened by the use of inlet port conduits which terminate approximately at the axis of the core.

Reduction in emissions of nitrogen oxides in some embodiments of this invention is not understood and cannot be explained in the chemical terms which in hindsight appear to explain the reduction of hydrocarbon and carbon monoxide emissions:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial cross section of a reactor of the type disclosed in U.S. Pat. No. 3,413,803 fitted with cylinder deflector embodiments of the invention.

FIGS. 2 and 3 are sectional views across the reactor at line 2 2 showing various deflector embodiments. FIG. 2 shows a single deflector which may be a partial cylinder or a partial sphere embodiment. FIG. 3 shows a double deflector which may be double partial cylinders or double partial spheres.

FIG. 4 is an axial cross section of one end of the reactor of FIG. 1 and FIG. 5 is a sectional view at line 3 3, both figures showing the optional preferred embodiment of an inlet port extension conduit.

FIG. 6 is a simplified line drawing representing the inside surfaces of core and deflector in a section at line 2 2 of FIG. 11. In this drawing the inlet port, not shown, is understood to enter vertically from the top.

DESCRIPTION OF THE INVENTION According to this invention there is provided means for the reduction of hydrocarbon, carbon monoxide and nitrogen oxides emissions from exhaust gas manifold reactors, hereinafter called reactors. The means comprise deflectors of new design preferably with modification of art means for introducing exhaust gas-air mixtures into the core, which modification comprises extension of inlet port conduits approximately to the axis of the core in order more certainly to direct at least a portion of the incoming gases directly into the deflectors. It is more preferred to constrict the inlet port extensions and most preferred, additionally to provide means to direct at least a part of the incoming stream from theinlet port extension axially toward the center of the core. The preferred means for this direction is a slot and tongue embodiment as hereinafter described.

Operable deflector shapes comprise hollow single or, two side by side, partial cylinders with end walls and with axes parallel to the axis of the reactor, or single, or side by side, partial spheres.

By partial cylinder is meant a cylinder a part of which is cut away along lines in the walls which describe a plane parallel to the axis of the cylinder. In double cylinder embodiments, the inside edges of the two partial cylinders intersect and are joined. By partial spheres is meant a sphere a part of which is cut away along a plane. In double partial sphere embodiments the partial spheres intersect at a point on their edges and are joined. It is preferred in this embodiment to divide the stream of incoming gases so as to direct approximately equal flows into each of the two partial spheres. The orientation of the parts of double deflector embodiments is fixed by an arithmetic relationship as described below.

In single and double partial cylinder embodiments the end walls may be straight or crescent shaped, the edge falling below the level of the edges of the cylinder to which they are attached. Additionally, in double partial cylinder configuraations, the end walls may be common to both partial cylinders in that they may extend from the outer edge of one partial cylinder to the outer edge of the other partial cylinder and may be straight or crescent shaped.

The dimensions of the deflectors are chosen so as to deflect at least most of the stream directed to them from the inlet conduit. Normally the diameter of single partial sphere embodiments and the width and length of cylinder embodiments are preferred to be about equal to the diameter of the inlet conduit. The diameter of double partial sphere embodiments is about equal to the stream dividing means, normally a forked inlet port extension conduit. In devices in which two inlet ports enter the core side by side it is preferred to use a cylinder embodiment to serve both conduits in which the width of the deflector is about equal to the inlet conduit diameter and the length is about equal to the sum of the inlet conduit diameters and the separating distance.

The preferred deflector shape is that of the double partial cylinder embodiment with straight end walls on each partial cylinder.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an embodiment of the invention installed in a modified reactor of US Pat. No. 3,413,803. The reactor is based on two concentric members, an outer shell 1 and an inner core 2. Outer shell 1 has integral shell extensions 3 and flanges 4 which are used to connect the outer shell of the reactor to the internal combustion engine adjacent to the exhaust ports of the engine. The illustrated reactor is designed for use with four exhaust ports of an engine. It is understood that reactors employing the same principles can be applied to engines having a different number of exhaust ports and that more than one reactor can be applied to engines with multi-cylinder banks such as V-type engines. Extensions 3 surround exhaust port extension conduits 5,6,7 and 8 which direct the flow of exhaust gases from the four exhaust ports of the engine (not shown) through outer shell 1 into the core 2 and to impingement on deflectors 9 and 10.

The deflectors 9 and 10 are illustrated in FIG. I in the single partial cylinder embodiment. Deflectors 9 and 10 direct the impinged gases upward in all embodiments away from the walls of core 2.

The upwardly deflected hot gases mix in the region 11 and somewhat to the outside of regions 12 and 13 while remaining out of scrubbing contact with the wall of core 2.

Outer shell 1 is, in the embodiment of FIG. 1, insulated on its inner surface by a layer of insulation 14. A dead air space and/or reflective insulation can be employed in place of solid insulation 14. When insulation 14 is used it is desirable to employ liners 15 to protect the insulation from erosion.

Exhaust gases leave core 2 in zones 16, which may be radial holes (not shown), and undergo sharp changes in direction due to impingement with end-cap 17. On passage through annular space 18 and further annular space (not shown) in the embodiment of copending application Ser. No. 63,101 filed 8-12-70, further oxidation occurs. The exhaust gases leave the reactor through pipe connection 19 which connects with annular space 18.

As reactors are subject to severe thermal stresses and consequent expansion, core 2 and extension conduits 5, 6, 7 and 8 are advantageously provided with slip fit attachment to outer shell 1. Core 2 is mounted within outer shell 1 by means of pins 20 which slip within the mounting in the outer shell thereby allowing core 2 to move in a longitudinal direction with respect to the outer shell during expansion and contraction due to temperature changes. The outer shell extensions 3 are tapered to provide an annular space 21 between exhaust port extension conduits 5, 6, 7 and 8 and outer shell extensions 3 to permit expansion and contraction.

In FIGS. 2 and 3 the deflectors and 10 are under inlet pOrt conduit 8 at line 2 2 in FIG. I. The embodiment of FIG. 2 which may be either a partial sphere or a partial cylinder is mounted in the wall of core 2 by conventional means such as welding and is arranged with sufficient clearance from liner 15 to permit thermal expansion and contraction. FIG. 3 represents a similar embodiment wherein the deflectors 9 and 10 are either a double partial cylinder or double partial sphere. In FIG. 2 the end wall of the partial cylinder embodiment is preferably straight, and the same preference applies to the end wall of each cylinder in the double partial cylinder embodiment shown in FIG. 3. The deflector embodiments may be interchanged within the same reactor.

FIGS. 4 and 5 illustrate in axial and sectional view a preferred embodiment of an inlet port extension conduit to inlet ports 5, 6, 7 and 8. The taper of the port extension conduit insures impingement on the deflectors of the gas stream leaving the end of the conduit.

Slot and Tongue 22 diverts a part of the stream from any inlet port extension conduit axially, normally toward the center of the core.

FIG. 6 shows the variables of distance and angle which define the inside wall relationships of core 2 and deflectors 9 and 10. a is the angle made by the outermost intercept of deflector 9 and core wall 2 and the outermost intercept of deflector 10 and core wall 2. [3 is the angle between the radius of a deflector and the radius of the core at the above intercept. The value of the angle is arithmetically equal to the inside angle of the tangents to the wall of deflector 9 or 10 and core wall 2. The angle is critical to operability as will be shown below. 4; is the outside angle of tangents to the walls of the double deflectors at intersection. r Is the radius of core 2 and r; is the radius of one deflector. As the core/deflector is symetrical in section, the radii of each lobe of double deflectors are the same.

OPERATION OF THE INVENTION The exhaust gas-air mixture entering a device in any embodiment is directed against the deflectors where its path is turned upward out of scrubbing heat transfer contact with the walls ofthe core 2. There appears to be conferred on the gases a screw-like motion which they retain at least for abrief but important moment near the axis of the core, during their movement through core 2. The hot gases do not come immediately in intimate contact with the relatively cold walls of the core but instead are insulated therefrom by a layer of more slowly moving and less hot semi-stagnant gases along the wall of core 2. Although the stagnant gases are less hot their residence time in core 2 is longer with the result that all gases leaving core 2 have lesser concentrations of oxidizable pollutants than is true with prior art devices.

In this manner there is imposed on the gases what might be called an ordered turbulence which ensures intimate mixing of the bulk of the exhaust gases and added air with each other without cooling them by contact with the relatively cold Walls of core 2. Disordered turbulence produced in prior art devices does not do this but instead mixes all gases in intimate scrubbing contact with the walls of core 2.

Extension of inlet ports 5, 6, 7, and 8 and installation of slot and tongue 22 diverters surprisingly reduces further the emissions of nitrogen oxides as well as those of hydrocarbons and carbon monoxide. Since exit from core 2 is principally through radial holes in the end-cap in the modification of FIG. 1 and as used in Example 3, it is apparent that at least a part of the gas stream turns back from its original direction of flow toward the center of core 2. It appears to do this, in view of the above emissions reduction, without resultant disordered turbulence and consequent heat loss.

Critical to the functioning of the devices of the invention in the above-described manner is the angle of the tangents at intersection of the deflectors and the core wall, shown as B in FIG. 6. It has been found that [3 must have an angle of at least in order effectively to divert the hot gases away from scrubbing contact with the core walls. All values ofB yield operable combinations up to about 100 at which point the turbulenc e appears to become disordered and the beneficial effects of the invention are lost.

As long as the value of B is held within the above limits, a. wide range in other variables produce operable combinations. For example, the ratio of radius of core 2 to the radius of deflectors 9 or 10 may vary from 0.5 to 2.5 and the value of (1) may vary from 0 to 180, it being understood that when qb is Ia single deflector embodiment is described. a

The above-described variables are by reason of geometry interrelated as required by equation I derived from first principles and which, within the above limitations comprise all operable embodiments of the invention.

cos /2 r,/r sin a/ sin (a/ -B) The symbols have the meanings shown in FIG. 6 and described herein.

As it is necessary to operability of the preferred double partial cylinder deflector embodiments that the separate partial cylinders intersect to form the angle d the further requirement of equation 2) is placed on equation 1).

0 r lr sin a/ sin (IBO-flX/ -B) l The relationships of equation 2) derive from the condition that the distance between centers of the deflectors 9 and 10 be equal or less than 2 r General equation (1) can comprise single deflector embodiments wherein the deflector is so shallow as to produce only marginal improvement over art devices. It has therefore been found desirable to limit the single deflector embodiments predicted by Equation I) to those wherein the distance between the deflector surface and a hypothetical circular extension of the core wall (shown as an interrupted line in FIG. 6), at their point of greatest separation is at least 4/10 the radius of the deflector. This relationship is conveniently ex pressed in Equation 4.

cos B O.32 r lr +0.6

This limitation does not apply to double deflector embodiments.

From the nature of the relationships expressed in Equation I it follows that of the variables a, B, (b and r lr any three may be independent within the limits set out, whereas the fourth is dependent on the others.

In the preferred embodiment of a single deflector device, a is about 33, ,8 about 50, (b is 180 and rm about 1.8. In the preferred double deflector devicea is about 139. B about 45, 1: about 70 and r,/r about 2.2. Most preferred is the double partial cylinder embodiment wherein the end walls of each partial cylinder are straight.

Descriptions of entire devices have been given for clarity. The improvements which embody the instant invention comprise the deflectors 9 and 10 and optionally the extensions to inlet port conduits 5, 6, 7 and 8 as shown in the drawings and herein described. These can be fabricated according to the methods which are well-known to those skilled in the art, and outlined, for example, in US. Pat. No. 3,413,803. Parts exposed to high temperature and erosion conditions are advantageously constructed of ceramic materials.

Whereas circular core and deflector sections have been shown modifications comprising curved sections not strictly circular are operable providing the abovedescribed limitations especially on the angle B are observed. Although deflectors 9 and 10 are shown as terminating in the wall of core 2, it is understood that as a matter of convenience, for example in welding, the walls of deflectors 9 and 10 may extend inside core 2 to an amount corresponding to about 5 rotation about the center of the deflector section.

The invention is further illustrated in the following examples, showing actual performance in connection with internal combustion engines.

EXAMPLE 1 The performance of a reactor without deflectors was compared with the performance ofa reactor containing a single partial sphere deflector for each port, and with a reactor containing a single partial cylinder deflector for each port. In the partial cylinder embodiment the end walls of each partial cylinder were straight.

The reactor used was that shown in FIG. 1 modified as disclosed in copending application Ser. No. 63,101 filed 8-12-70, wherein radial holes were cut in the core end partition and radially in the side walls of core 2 in the region of 12 and 13. A second annular flow channel and dead air and reflective insulation were provided in the place of solid insulation 14. All parts of the device were of welded steel construction.

The inside diameter of core 2 was 2 A; inches. The tests involved the use of two reactors, one for each band of cylinders, and were carried out on a 1969 350 cu. in. displacement V-8 Chevrolet pick-up truck with automatic transmission.

Air was injected into the exhaust gas stream upstream from the reactors essentially according to the process of Tifft by means of a vane pump of 19.3 cu. in. displacement driven by the engine at a drive ratio of 1.54 to 1. The test resulting in weighted analyses of emissions during programmed series of driving conditions in dynomometer, was that of the California Test Procedures and Criteria for Motor Vehicle Exhaust Emission Control of the Motor Vehicle Control Board of the State of California dated May 16, 1961 and revised Jan. 23, 1964.

The parameters of the deflector sections and the results in replicate are shown in Table 1.

From the results it is seen that emissions of carbon monoxide were reduced an average of 35 percent by the partial sphere deflector embodiment and 41 percent by the partial cylinder embodiment. Hydrocarbon emissions were not significantly affected as the levels achieved by the reactor without deflectors are already quite low, being substantially below the 1970 goals of ppm set by the above-cited Agency.

EXAMPLE 2 The performance of a reactor without deflectors was compared with the performance of a reactor containing the double partial cylinder embodiment of the invention.

The deflectors serving single exhaust gas inlet ports were in this example longer than preferred in that they were about 2.5 times the diameter of the inlet ports. The deflectors serving double port were of the preferred lengths as described above and as shown in F16.

The test was that of Example 1. The reactor had an inside core diameter of 2 "/8 inches and was of the same design as Example 1. The test vehicle was a 1970 350 cu. in. displacement V-8 Chevrolet passenger automobile.

Typical emission levels from the reactor without deflectors but with more efficient reflective heat shielding, description of deflector section parameters, and results of the tests are given in Table 2.

The results demonstrate substantial reduction in both hydrocarbon and carbon monoxide in a somewhat less efficient reactor-engine combination than in Example 1 with somewhat less reactor insulation.

EXAMPLE 3 The efiicacy of inlet port conduit extension and deflection of a part of the inlet gas stream axially toward the center of the core, as shown in FIGS. 4 and 5 was demonstrated as follows:

the reactor of core diameter 3 A; inches was of the double partial cylinder embodiment wherein the deflectors were of the preferred length being about equal to the diameter of the inlet ports. The deflector section parameters were: a 1l2.5, [3 39, d: 72, and r,r 2.2.

The tests were carried out on the automobile of Example 2 according to the Federal Testing Procedure as described in Federal Register Vol. 35 No. 219 part 11 dated Nov. 10, 1970. The control experiment consisted in test of the reactor with the same deflectors but without inlet port conduit extensions.

The results, reported in the units recommended by the Federal Register reference, are shown in Table 3.

TABLE 3 Hydrocarbons Carbon Monoxide Nitrogen Oxides (Grams/mi.) Grams/mi.) (Grams/mi.)

Control 0.118 14.7 1.07 Extended Conduits not measurable 6.85 0.92

9 It has further been found that by operating the engine at slightly richer fuel ratios, the emissions especially of nitrogen oxides can be further reduced. Under these conditions, the average of seven tests showed nitrogen oxide levels of 0.51 grams/mi.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An improved exhaust gas reactor for reducing the undesirable emissions from an internal combustion engine, said reactor comprising an elongated casing enclosing a cylindrical core, having a radius, core walls and a longitudinal axis, having an inlet directing exhaust gas through the casing, into and across the core and having an outlet through the core and easing, said improvement comprising gas deflector means, circular in cross-section, having a radius and positioned within said core across from and in concave relationship to the exhaust gas inlet to the core, intersecting the core wall at an angle and in partial replacement of said wall, said deflector means being positioned such that the inside angle [3, formed by the tangents to the core wall and deflector surface at the point of their intersection is no less than 20 and no more than 100, and the ratio of the core radius to deflector radius is between 0.5 and 2.5, whereby scrubbing heat transfer contact between the exhaust gas and core walls is minimized.

2. A reactor of claim 1 wherein two gas deflector means are positioned within the core across from and in concave relationship to each exhaust gas inlet to the core, and wherein the deflector cross sections are defined by the equation cos (M2 r,/r sin 01/ sin (l80( /z-B) wherein r, is the radius of the core;

r is the radius of each deflector;

r,/r is between 0.5 and 2.5;

d; is the angle of the tangents at the intersection of the deflectors and is between and 180;

B is the inside angle formed by tangents to the core wall and deflector surface at the point of their intersection and is between 20 and 100; and

a is the angle made by the outermost intercept of one deflector with the core wall and the outermost intercept of the other deflector with the core wall.

3. A reactor of claim 2 wherein the deflector means are partial cylinders having end walls, each partial cylinder being defined by the intersection of a right circular cylinder by a plane parallel to its axis, a is about 139, B is about 45, d) is about and r /r is about 2.2.

4. A reactor of claim 3 wherein the end walls of each partial cylinder are straight.

5. A reactor of claim 1 wherein a single gas deflector means is positioned within the core across from and in concave relationship to each exhaust gas inlet to the core, the distance between the deflector surface and a hypothetical circular extension of the core wall at their point of greatest separation being at least 4/10 the radius of the deflector.

6. A reactor of claim 5 wherein the gas deflector means is a partial cylinder having end walls, said partial cylinder being defined by the intersection of a right cir cular cylinder by a plane parallel to its axis, the angle a, made by the outermost intercept of one side of the deflector with the core wall and the outermost intercept of the opposite side of the deflector with the core wall is about 33,

the inside angle B formed by the tangents at the point of intersection of the deflector and the core wall is about 50, and

the ratio of the radius of the core, r,, to the radius of the deflector, r is about L8.

7. A reactor of claim 6 wherein the end walls of the partial cylinder are straight.

8. A reactor of claim 1 wherein the inlet ports are conduits which terminate approximately at the axis of the core.

9. A reactor of claim 8 wherein the inlet port conduits are constricted and contain means for directing a part of the incoming gas stream axially toward the center of the core.

10. A reactor of claim 9 wherein the means for directing a part of the incoming gas stream consists of a slot across the conduit opening toward the core center and a tongue extending into the conduit from the downstream side of the slot.

11. A reactor of claim 8 wherein the inlet port conduits are constricted and direct a substantial part of the incoming gas against the deflector surface. 

2. A reactor of claim 1 wherein two gas deflector means are positioned within the core across from and in concave relationship to each exhaust gas inlet to the core, and wherein the deflector cross sections are defined by the equation cos phi /2 r1/r2 sin Alpha /2 - sin (180- Alpha /2- Beta ) wherein r1 is the radius of the core; r2 is the radius of each deflector; r1/r2 is between 0.5 and 2.5; phi is the angle of the tangents at the intersection of the deflectors and is between 0* and 180*; Beta is the inside angle formed by tangents to the core wall and deflector surface at the point of their intersection and is between 20* and 100*; and Alpha is the angle made by the outermost intercept of one deflector with the core wall and the outermost intercept of the other deflector with the core wall.
 3. A reactor of claim 2 wherein the deflector means are partial cylinders having end walls, each partial cylinder being defined by the intersection of a right circular cylinder by a plane parallel to its axis, Alpha is about 139*, Beta is about 45*, phi is about 70* and r1/r2 is about 2.2.
 4. A reactor of claim 3 wherein the end walls of each partial cylinder are straight.
 5. A reactor of claim 1 wherein a single gas deflector means is positioned within the core across from and in concave relationship to each exhaust gas inlet to the core, the distance between the deflector surface and a hypothetical circular extension of the core wall at their point of greatest separation being at least 4/10 the radius of the deflector.
 6. A reactor of claim 5 wherein the gas deflector means is a partial cylinder having end walls, said partial cylinder being defined by the intersection of a right circular cylinder by a plane parallel to its axis, the angle Alpha , made by the outermost intercept of one side of the deflector with the core wall and the outermost intercept of the opposite side of the deflector with the core wall is about 33*, the inside angle Beta formed by the tangents at the point of intersection of the deflector and the core wall is about 50*, and the ratio of the radius of the core, r1, to the radius of the deflector, r2, is about 1.8.
 7. A reActor of claim 6 wherein the end walls of the partial cylinder are straight.
 8. A reactor of claim 1 wherein the inlet ports are conduits which terminate approximately at the axis of the core.
 9. A reactor of claim 8 wherein the inlet port conduits are constricted and contain means for directing a part of the incoming gas stream axially toward the center of the core.
 10. A reactor of claim 9 wherein the means for directing a part of the incoming gas stream consists of a slot across the conduit opening toward the core center and a tongue extending into the conduit from the downstream side of the slot.
 11. A reactor of claim 8 wherein the inlet port conduits are constricted and direct a substantial part of the incoming gas against the deflector surface. 